In buildings having a warm air heating system such as a forced air furnace with a gas or oil fired combustion chamber, there is a need for a controlled air supply to enter the interior of the building. In a house having such a heating system, it is considered desirable to reduce heat losses by sealing the openings, as by caulking around doors and windows and the like. If the house is sealed tightly, there is a chance inadequate combustion air will be supplied to the furnace resulting in the production of carbon monoxide, possibly at a dangerous level. Thus, there should be a provision for the supply of additional amounts of combustion air to enter without total dependence upon leakage through the walls, windows and doors of the house. Further, in the typical house there is an air loss by convection through fireplace chimneys, discharge by kitchen and bathroom fans, dryers and other such causes. This results in the depletion of interior air that contributes to a pressure differential being created between the inside and outside of the house. This differential in pressure tends to increase the influx of cold air through leakage in the walls with a concomitant energy loss. It is desirable to provide a supply of replacement or make-up air within a controlled environment to the interior of the house so as to equalize or tend to equalize the interior and exterior air pressure.
In the prior art, several systems and devices have been proposed for supplying make-up air to a building. Arrangements for supplying fresh air to the return air duct of a furnace through a pressure actuated damper is shown in the Dibert U.S. Pat. No. 3,204,870. Similar arrangements are shown in Elliott U.S. Pat. No. 2,721,033, Graden U.S. Pat. No. 4,138,062 and Powers U.S. Pat. No. 2,225,181.
The prior art also includes an arrangement for supplying outside air to the combustion chamber of a furnace. The Dyer U.S. Pat. No. 3,805,764 describes a fresh air supply duct which is connected directly to the furnace structure for supplying combustion air. Similar arrangements are disclosed in Schossow U.S. Pat. No. 4,171,089 and Grott U.S. Pat. No. 4,121,562.
It is also known in the prior art to supply combustion air to the combustion chamber and to supply draft air to the chimney. Such an arrangement is disclosed in the Dingwall U.S. Pat. No. 4,038,963 wherein a common air duct communicates with the exterior of the building and separate conduits extend from the duct to the chimney and to the combustion chamber. Similar arrangements are shown in Stramaglia U.S. Pat. No. 2,242,802 and the Bellaff U.S. Pat. No. 4,285,325.
In co-pending patent application Ser. No. 540,641 filed Oct. 11, 1983, by the inventor of this invention, a control unit for make-up air and combustion air is disclosed. The control unit has a baffle with a combustion air inlet and a make-up air inlet and is adapted to be mounted on the outside wall of the building. The baffle includes a restrictor plate with openings aligned with the combustion air and make-up air inlets. The baffle includes a damper in the make-up air inlet which opens in response to reduced pressure in the furnace return air duct so that the inside pressure tends to be equalized with the outside pressure. The combustion air inlet is unrestricted and is open at all times to admit outside air and thus when the furnace is running additional combustion air is supplied.
In general, it is an objective of this invention to provide an improved air circulating system for controlled supply of make-up and combustion air as required by forced air furnaces and air conditioner systems.